In recent years, with the spread of computers, ink jet printers have been widely used to print on paper, film, cloth, etc. at offices as well as at home.
Examples of ink jet recording method include a method which allows a piezoelectric element to give pressure that causes a droplet to be ejected, a method which comprises heating the ink to generate bubbles, causing a droplet to be ejected, a method involving the use of ultrasonic wave, and a method which uses electrostatic force to suck and discharge a droplet. As inks for these ink jet recording methods there are used aqueous inks, oil-based inks and solid (melt type) inks. Among these inks, aqueous inks are mainly used from the standpoint of producibility, handleability, odor, safety, etc.
The coloring agents to be incorporated in these inks for ink jet recording are required to exhibit a high solubility in solvents, allow a high density recording and have a good hue and an excellent fastness to light, heat, air, water and chemical, a good fixability to image-receiving materials, difficulty in running, an excellent preservability, no toxicity and a high purity and be available at a low cost. However, it is extremely difficult to seek coloring agents meeting these requirements to a high extent. In particular, coloring agents having a good magenta hue and cyan hue and an excellent light fastness have been keenly desired.
Various dyes and pigments have been already proposed for ink jet recording and have been actually used. However, no coloring agents meeting all these requirements have been found yet. Known dyes and pigments provided with color index (C.I.) can difficultly satisfy both the hue and fastness requirements for inks for ink jet recording. No magenta dyes having an excellent hue and a satisfactory fastness have been obtained yet.
On the other hand, an ink jet recording method involving recording with an ink set comprising an ink (e.g., dark yellow ink) comprising a small amount of dyes (or pigments) having different hues incorporated in admixture in a main dye (or pigment) has been proposed. However, it was found disadvantageous in that when an ink comprising a plurality of dyes (or pigments) incorporated in admixture therein is used, the recorded image undergoes color tone change with time and the degree of change differs with the image density due to the difference in dye fastness among the dyes (or pigments) in the ink composition and probably due to the interaction of the dyes (or pigments). These troubles cause an undesirable complex color balance change that cannot be corrected even by controlling the ink jet printer by an image processing soft ware. As a result, neutral color (also referred to as “gray”), which is a base of color image quality, is tinted, remarkably deteriorating the image quality.
The deterioration of quality of recorded image with time is accelerated by exposure to high temperature and humidity or an oxidizing atmosphere or irradiation with light at high illuminance. Accordingly, the dye (or pigment) to be incorporated in the ink composition has been required to have excellent heat stability, light fastness and oxidation resistance and undergo no tint change of neutral color with time, i.e., no change of color balance.